How do I get full by eating portion sizes?

I dont understand how I can get full by only eating 1 cup of brown rice with veggies. Like how do I get full if I follow recommended serving sizes ☹
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How do I be okay eating so very little.
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I'm watching videos and just realized I've not been doing well on my portion sizes and I feel terrible. Just started my diet on Monday. Will I be okay?

I've been eating so healthy. I just feel it's a waste on my portion sizes like oils and salad dressings. I feel so terrible
How do I get full by eating portion sizes?
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