Shiny: How to prevent selectInput from being reset by selecting the second selectInput

This builds on a question I ran into here , but I'm simplifying the example to make it easier to read (and therefore easier for future searchers).

reproducible example

Here is the data:

library(tidyverse)
library(shiny)

food_table <- structure(list(Food_category = c("Fruit", "Fruit", "Fruit", "Fruit", 
                                               "Vegetable", "Vegetable", "Fruit", "Fruit", "Fruit", "Vegetable"
), Food = c("Granny Smith apple", "McIntosh apple", "Avocado", 
            "Blueberries", "Broccoli, steamed", "Cucumber", "Banana", "Cherries", 
            "Nectarine", "Red onion"), Serving_Size = c(1, 1, 0.333333333333333, 
                                                        1, 1, 1, 1, 1, 1, 1), Serving_Unit = c("apple", "apple", "avocado", 
                                                                                               "cup", "cup", "cup", "banana", "cup", "nectarine", "cup"), Carbs_per_Serving = c(25, 
                                                                                                                                                                                25, 4, 21, 3.5, 4, 27, 25, 15, 11)), row.names = c(NA, -10L), class = c("tbl_df", 
                                                                                                                                                                                                                                                        "tbl", "data.frame"))


(food_table)

   Food_category Food               Serving_Size Serving_Unit Carbs_per_Serving
   <chr>         <chr>                     <dbl> <chr>                    <dbl>
 1 Fruit         Granny Smith apple        1     apple                     25  
 2 Fruit         McIntosh apple            1     apple                     25  
 3 Fruit         Avocado                   0.333 avocado                    4  
 4 Fruit         Blueberries               1     cup                       21  
 5 Vegetable     Broccoli, steamed         1     cup                        3.5
 6 Vegetable     Cucumber                  1     cup                        4  
 7 Fruit         Banana                    1     banana                    27  
 8 Fruit         Cherries                  1     cup                       25  
 9 Fruit         Nectarine                 1     nectarine                 15  
10 Vegetable     Red onion                 1     cup                       11  

I have a shiny app which has multiple inputs. This works, except when a new selection is made in the second food category box, the food selection in the first row changes back to the first element. In other words, if I select "Fruit" in the first row, then "Avocado" and "1", then when I go to the second row and select "Vegetables", the selected food item changes from "Avocado" " becomes "Grandma "Smith Apple". I'm trying to figure out how to prevent the row from resetting after making a selection.

Here is the stripped down shiny code:

# Table filters
categories <- sort(unique(food_table$Food_category))
foods      <- sort(unique(food_table$Food))
unit       <- sort(unique(food_table$Serving_Unit))

# Create Shiny app 

   # Define UI
    ui <- fluidPage(headerPanel(strong("Carbohydrate Calculator")),
                    
                    fluidRow(
                      column(
                        width = 3,
                        selectInput(
                          inputId = 'cat_1',
                          label   = 'Food Category',
                          choices = c("None", categories)
                        )),
                      column(
                        width = 3,
                        selectInput(
                          inputId = 'food_1',
                          label   = 'Food Item',
                          choices = foods
                        )),
                      column(
                        width = 3,
                        numericInput(
                          inputId = "actual_serving_1",
                          label = "How much?",
                          value = "",
                          min = 0,
                          max = 100
                        ))
                    ),
                    fluidRow(
                      column(
                        width = 3,
                        selectInput(
                          inputId = 'cat_2',
                          label   = 'Food Category',
                          choices = c("None", categories)
                        )),
                      column(
                        width = 3,
                        selectInput(
                          inputId = 'food_2',
                          label   = 'Food Item',
                          choices = foods
                        )),
                      column(
                        width = 3,
                        numericInput(
                          inputId = "actual_serving_2",
                          label = "How much?",
                          value = "",
                          min = 0,
                          max = 100
                        ))
                    ),
                    
                    column(8,
                           tableOutput("my_table"),
                           span(textOutput("my_message"), style="color:red")
                    ) # Column close
                    
    )                 # fluidPage close
    
    
    
    # Define server logic required to draw a histogram
    server <- function(input, output, session) {
      
      
      food_table_1 <- reactive({
        food_table %>%
          filter(Food_category == input$cat_1) %>% 
          filter(Food == input$food_1) %>% 
          mutate(Actual_amount = input$actual_serving_1) 
      })
      
      food_table_2 <- reactive({
        food_table %>%
          filter(Food_category == input$cat_2) %>% 
          filter(Food == input$food_2) %>% 
          mutate(Actual_amount = input$actual_serving_2) 
      })
      
    
      
      # Combine selections into a single table
      combined_tables <- reactive({
        do.call("rbind", list(food_table_1(),
                              food_table_2()
        )
        ) %>% 
          mutate(Total_Carbs_grams = Carbs_per_Serving * Actual_amount / Serving_Size) %>% 
          select(Food_category, Food, Serving_Size, Serving_Unit, Actual_amount, Carbs_per_Serving, Total_Carbs_grams, everything())
      })
      
      
      # Render Output table
      output$my_table <- renderTable({
        
        combined_tables()
        
      })
      
      
      
      # Create observe function which updates the second selectInput when the first selectInput is changed
      observe({
        
        updateSelectInput(
          session,
          inputId = "food_1",
          choices = food_table %>% filter(Food_category == input$cat_1) %>% pull(Food)
        )
        
        updateSelectInput(
          session,
          inputId = "food_2",
          choices = food_table %>% filter(Food_category == input$cat_2) %>% pull(Food)
        )
        
        
      }) # Observe close
    }    # Server close
    
    
    
    # Run the application 
    shinyApp(ui = ui, server = server)